Quantum Consolation Physicists Are Still Scratching Their Heads

Richard Feynman and Yang Cen Ning
Richard Feynman and Yang Cen Ning

Our editorial on quantum physics (August 30) begins with a quote from Richard Feynman, who says “nobody understands quantum mechanics” and then says "that's not true anymore". Quantum theory was developed in the 1920s and 1930s by many physicists, including Dirac, Erwin Schrödinger, and Werner Heisenberg, and Dirac made his work relativistic.

Our editors say it is absurd to say that quantum mechanics was not understood 50 years ago, but is now understood. There have of course been advances in our understanding of quantum phenomena, but the conceptual framework of quantum physics has remained intact. Your examples of nuclear power plants, medical scans, and lasers include simple applications of quantum mechanics that were understood 50 years ago.

The greatest advance in the understanding of quantum physics during this period was the notion that quantum physics could not be local. It is a theorem of John Bell of CERN. That is, it allows phenomena to be associated at arbitrarily large distances from each other. This has now been demonstrated experimentally and has led to what is known as quantum entanglement, which is important in the development of quantum computers. But even these ideas were discussed by Albert Einstein and his colleagues in 1935.

Our editorial goes on to say that “subatomic particles do not follow a path that can be drawn.”

If so, how could protons travel through the Large Hadron Collider at Cern and hit their target so that experiments could be carried out?

The editors agree with Phillip Ball, who writes in Physics World that "a century after quantum mechanics was conceived, it still leaves our heads scratching." There are many speculative suggestions in the discussion, but none of them have consensus support.

Whoever wrote this editorial doesn't understand what Richard Feynman means when he says that no one really understands quantum mechanics.

Being able to build a smartphone, a nuclear weapon, or an MRI machine doesn't require an understanding of quantum mechanics in the sense he meant.

It requires physical signs to set up equations and mathematical signs to find or approximate solutions to them.

Any competent physicist has done these calculations for at least 50 years.

What Feynman meant was that for quantum mechanics, no one had the kind of intuitive understanding physicists were trying to gain of what really happened in the world.

All we can do is shut up and calculate, or get lost in a land of never, ever competing but empirically equivalent interpretations.

Perhaps Carlo Rovelli's relational interpretation of quantum mechanics provides the intuitive understanding we want to have. However, I doubt this, and I don't think Rovelli claims it. It perhaps makes testable predictions that might distinguish it from other interpretations, and is therefore more science than philosophy (our author has no objections to philosophy).

It is as true today as it was when Feynman said in 1964 that no one (or almost no one) really understood quantum mechanics. And now, as then, a competent physicist doesn't need the kind of understanding Feynman wanted to use the theory for. Indeed, there is no strong reason to believe that the human mind should be equipped to understand it.

Source: theguardian.com/science/2021/sep/03/quantum-of-solace-even-physicists-are-still-scratching-their-heads

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